Investigations to discover the intimate factors involved in the initiation and development of neoplasia are explored by means of animal experiments in various species. The studies utilized a number of chemical carcinogens administered to animals under varying conditions of diet, endocrine situation or immunological status, so as to gain insight into controlling mechanisms in the initiation and development of chemically induced tumors. Further efforts deal in the development of systems which lead to the prevention of the processes of chemical carcinogenesis in a study of the mechanisms related thereto.